激励器结构对三电极等离子体高能合成射流流场及其冲量特性的影响

摘要

等离子体激励器以其结构简单、响应速度快、环境适应性强等优势，已成为主动流动控制技术和流体力学研究的前沿与热点。相比于传统两电极激励器，三电极等离子体高能合成射流激励器具有更高的能量效率，形成射流冲量更大，有望成为新型快响应直接力产生装置。为揭示激励器结构对射流流场和冲量特性的影响规律，进而优化激励器结构参数，利用电参数测量装置、高速阴影系统及自主设计的单丝扭摆式微冲量测量系统对不同射流孔径、腔体体积和电极间距的三电极激励器放电特性、射流流场及其冲量进行了实验研究。为对比激励器在不同工况条件下的工作特性，定义无量纲能量沉积ε和无量纲射流冲量 I *，并分析了激励器结构参数对ε和 I *的影响。结果表明对于给定无量纲能量沉积ε，激励器存在最优射流孔径；激励器无量纲能量沉积ε和无量纲射流冲量I *随腔体体积增加而减小，随激励器电极间距增加而增加；射流强度及其流场影响区域随腔体体积增加而减小，随激励器电极间距增加而增加。对比不同腔体体积和电极间距工况条件下 I *随ε的变化可知，为设计具有较好射流冲量水平的激励器，在相同无量纲能量沉积ε条件下，应尽量增大激励器无量纲射流冲量 I *。当设计激励器无量纲能量沉积ε小于初始工况时，应增大初始工况激励器腔体体积使无量纲能量沉积ε降低至设计值；当设计激励器无量纲能量沉积ε大于初始工况时，应增大初始工况激励器电极间距使无量纲能量沉积ε增加至设计值，使设计激励器具有较好的射流冲量水平。%Plasma actuators have been become the research focus in flow control and fluid dynamic fields because of the advantages of simplicity,fast response and robustness.Compared with typical two-electrode actuator,three-electrode Plasma Synthetic Jet Actuator (TE-PSJA) possesses the advantages of higher energy efficiency and bigger jet impulse,and has potential to be adopted as a fast-response direct force generation device.In order to reveal the effects of geometric parameters on the flow field and impulse,discharge characteristic,flow field and impulse of TE-PSJA with different orifices,volumes and electrode gaps were experimentally studied using electric parameter measurement device,high-speed shadowgraphy and single line torsion pendulum system.In order to compared the working characteristics of the actuator in different conditions,dimensionless energy depositionε and dimensionless jet impulse I * were defined,and the effects of geometric parameters onεand I * were analyzed.Results showed that the best jet orifice diameter is existed,ε and I * decreases as volumes increase,but increases as electrode gaps increase,strength and affected area of the jet decrease as volumes increase,while increase as electrode gaps increase.A similar flow structure which contains a mushroom-shaped jet and a spherically symmetric precursor shock above the jet front was observed.Compared with the variation of I * with ε on the different volumes and electrode gaps conditions,it can be concluded that in order to design actuators which possessed better jet impulse level, the dimensionless jet impulse I * should be increased as possible with the sameε.The cavity volume should be increased so as the dimensionless energy depositionεis to be the design value when the dimensionless energy deposition is less than the initial case.On the contrary,the electrode gaps should be increased so as the dimensionless energy depositionε be the design value when the dimensionless energy deposition is larger than the initial case.